The present invention relates to the art of optical integrated circuits and more particularly to apparatus and methods for aligning optical fiber arrays with optical integrated circuits.
BACKGROUND OF THE INVENTION
Optical integrated circuits (OICs) include devices such as 1xc3x97N optical splitters, optical switches, wavelength division multiplexers (WDMs), and the like, which are used in a variety of applications. For instance, traditional signal exchanges within telecommunications networks and data communications networks using transmission of electrical signals via electrically conductive lines are being replaced with optical fibers and circuits through which optical (e.g., light) signals are transmitted. Such optical circuits may have a planar structure, commonly known as planar lightwave circuits (PLCs), in which one or more optical circuits in the OIC can be used for routing optical signals from one of a number of parallel input optical fibers to any one of a number of parallel output optical fibers.
The input and output optical fibers are typically formed in a group or array of many such fibers (e.g., 48), where the fiber array is connected to a planar substrate (e.g., an integrated circuit chip) to transmit or receive light to or from waveguides in the optical circuit. Light from the optical fibers is then provided to optical circuitry via the waveguides, wherein the optical circuitry may include switches, multiplexers, modulators, or other optical circuitry. The waveguides comprise optical paths deposited on the chip, which are made from glass or other transmissive media such as optical polymers, wherein the waveguides have a higher index of refraction than the chip substrate in order to guide light to or from the optical fibers in the array. The waveguide ends are commonly formed on a sidewall of the optical circuit, whereat the optical fiber ends may be connected with the waveguides. The connection of optical fibers to the optical integrated circuit is sometimes referred to as xe2x80x9cpigtailingxe2x80x9d, where an optical fiber array attached to the optical circuit appears as a pigtail.
In the pigtailing process, the ends of the optical fibers in the array must be aligned with the ends of the waveguides in the OIC, in order to ensure proper transmission of light therebetween. Conventional techniques for such alignment have included one at a time alignment and attachment of individual optical fibers, which is time consuming and not ideally suited for higher volume production of pigtailed devices. Other conventional techniques employ V-grooves etched in the substrate, in which the optical fibers may be placed for lateral alignment with the waveguides. However, inaccuracies in the lithographic and etching processes limit the applications of alignment by this methodology.
Active alignment techniques include monitoring the optical transmission of the connection visually or observing the relative positions of the waveguide cores while moving the optical fibers relative to the planar waveguides. Such transmission monitoring can be performed using a light source providing light to one or more fiber ends, and a light detector. It has been found that such active alignment procedures typically produce lower loss interconnections, but result in a higher cost per interconnection than passive alignment techniques. For example, one or more dedicated waveguides may be provided in an optical integrated circuit for providing light from an input array directly to an output array. Corresponding input and output array fibers are connected to a light source and a light detector, and the input and output arrays are moved relative to the OIC until light from the light source (e.g., at the input array) is detected (e.g., at the output array), thereby indicating proper alignment of both the input and output fibers.
An example of a conventional OIC alignment system 2 is illustrated in FIG. 1, for aligning input and output optical fiber arrays 4 and 6 to an optical integrated circuit 8. The OIC 8 includes dedicated alignment waveguides 20 and 22 at the outermost ends of the waveguide rows providing optical paths between the outermost fibers of the arrays 4 and 6. The alignment system 2 further includes light sources 40 and 44 providing light to the input fibers 30 and 34, respectively, of the array 4, as well as and light detectors 42 and 46 receiving light from the output array fibers 32 and 36, respectively. As can be seen in FIG. 1, the system 2 suffers from several drawbacks, which render the technique expensive and/or impractical in a manufacturing setting. One such drawback, is that the input fiber array 4 must be aligned in order to verify the output array alignment, while at the same time, the output array 6 must be aligned to verify alignment of the input array.
Another variant includes connecting the light source 40 to a fiber (e.g., fiber 30) in input array 4 and moving the array 4 relative to the OIC 8 while manufacturing personnel manually view the output end of the dedicated waveguide 20 (e.g., without the output array 6) to determine when light is transmitted, thereby indicating alignment of the input fiber 30 with the dedicated waveguide 20. Thereafter, a fiber 32 in the output array 6 is connected to light detector 42, and is moved until light is detected, thus indicating alignment of the output array fiber 32 with the dedicated waveguide 20. This process is time consuming and requires human intervention, which is impractical in high volume manufacturing environments. Thus, there remains a need for apparatus and methodologies by which fiber array pigtailing may be performed in an expeditious automated fashion.
The following presents a simplified summary of the invention in order to provide a basic understanding of some aspects of the invention. This summary is not an extensive overview of the invention. It is intended to neither identify key or critical elements of the invention nor delineate the scope of the invention. Rather, the sole purpose of this summary is to present some concepts of the invention in a simplified form as a prelude to the more detailed description that is presented hereinafter. The present invention provides optical circuits with optical alignment guides and methods for alignment of optical fiber arrays with optical circuits by which the above mentioned and other problems may be overcome or mitigated.
One aspect of the invention provides an optical integrated circuit (OIC) comprising a loop around optical alignment guide located in a fixed position relative to an input or an output end of the OIC, wherein the alignment guide has first and second ends facing in the same direction and operative to interface with first and second optical fibers, with an optical path between the first and second ends. The alignment guide can loop light from one fiber in an array back to another fiber in the same array, thereby facilitating alignment of an individual array with the OIC independent of alignment (e.g., or the presence) of another array.
Thus, for example, an input fiber array can be aligned and pigtailed to an OIC independently from alignment of an output array to the OIC. In addition, the alignment guide allows expeditious alignment and attachment of such arrays (e.g., pigtailing) without human intervention, thereby facilitating automated pigtailing operations in a manufacturing setting. More than one such loop type alignment guide can be provided in an OIC, for example, whereby alignment guides are positioned at the ends of rows of input and/or output active waveguides.
Another aspect of the invention provides methodologies for aligning an optical fiber array with at least one waveguide in an optical integrated circuit. The methods comprise providing an optical alignment guide in the optical integrated circuit having an optical path extending between its first and second ends, the first and second ends of the optical alignment guide being located in a fixed position relative to the waveguide, providing light to a first end of a first optical fiber in the array, and detecting light from a first end of a second optical fiber in the array, and positioning the array such that light is detected at the first end of the second optical fiber.
In addition, a second optical alignment guide may be provided in the optical integrated circuit having an optical path extending between its first and second ends, the first and second ends of the second optical alignment guide being located in a second fixed position relative to at least one waveguide. In this variant, the method may comprise providing light to a first end of a third optical fiber in the array, and detecting light from a first end of a fourth optical fiber in the array, and positioning the array such that light is detected at the first ends of the second and fourth optical fibers. Yet another aspect of the invention relates to making an optical integrated circuit by providing one or more loop around alignment guides with ends facing the same direction and an optical path therebetween.
Yet another aspect of the invention provides systems for aligning an optical fiber array with an optical integrated circuit, comprising the optical integrated circuit containing an optical alignment guide having an optical path extending between first and second ends, wherein the first and second ends face the same direction and are located in a fixed position relative to at least one waveguide; the optical fiber array comprising a first optical fiber having a first and second ends and a second optical fiber having a first and second ends, and a third optical fiber having a first and second ends; a light source for directing light into the first end of the first optical fiber; and a light detector for detecting light from the first end of the second optical fiber.